Some Rookie Questions and and Picture for C&C

Hey guys i just got a new Canon 30d for xmas. I know a lot about what each setting does and like how to compensate one setting for another and all that stuff.

I AM USING A "CANON ZOOM LENS EF 70-210."

First Question: I was out shooting birds today and I couldnt really get a crisp shot on a bird. Like I got it in the frame and it was focused (i used infinite manual focus) but when I look at it full screen on the computer, it is just never as clear as "the professionals." What can I do to get clearer pictures? My shutter speed is at about 6000 and my aperture is a f/4. ISO is idk? somwhere around 400-800. Do I need a new lens?

Here are some examples:

Also in these pictures, how would I bring out more color? I am using a polarized filter BTW.